There is increasing need to observe an object more intuitively in an electron microscope by reconstructing a three-dimensional structure from two-dimensional images obtained and, moreover, to extract and quantify any point in a reconstructed image. Various methods have been proposed to carry out such an observation.
For example, Non-Patent Document 1 discloses a back projection method of obtaining continuous tilted two-dimensional images by continuously tilting an object to be observed and reconstructing a three-dimensional image by doing back-projecting for each of the obtained continuous tilted two-dimensional images from the tilt angle at the time of obtainment, and Non-Patent Document 2 discloses a method of regarding the above-mentioned continuous tilted two-dimensional images as true value images in respective projection directions and then algebraically reconstructing an unknown three-dimensional image such that the errors between the results obtained by projecting the three-dimensional image in respective directions and the true values are minimum.
Additionally, Non-Patent Document 3 describes a dots concentration reconstruction technique, which is based on a concept that an image is a collection of dots, for optimizing the positions of dots in a three-dimensional image on the basis of the above-described continuous tilted two-dimensional images; and Non-Patent Document 4 describes a discrete algebraic reconstruction technique (DART) for creating a reconstructed image as a reference image using an algebraic reconstruction technique, dividing the reconstructed image into sections at a certain threshold value, and then reconstructing the image algebraically again using the information on the sections.